Specifications

www.axcera.com • 724-873 -1500
UHF Solid State Transmitters
High Performance
Exciter
The exciter, designed and
built by Axcera, contains the
circuitry to convert the input
video and audio signals to a
combined, modulated RF
signal which drives two very
linear phase and gain
modules. An optional
second exciter with
automatic exciter switcher is
available for added
redundancy.
Video/Visual Modulation
The video signal is processed
in several ways prior to
modulation. Sync tip
clamping is provided to
restore proper DC level.
Sync and white clipping are
also included to limit video
transient faults. Back porch
clamping is also available for
some scrambling systems.
The video signal is then
applied to a double
balanced diode modulator,
providing modulation
UHF Solid State Transmitters
capability to 1% at standard
intermediate frequency (IF).
A SAW filter is employed
for precise sideband
filtering with minimal group
delay error.
Audio/Aural Modulation
The audio signal is applied to
a very wideband, linear FM
modulator which operates at
intercarrier frequency (4.5
MHz for system M). The
high performance modulator
accepts a full range of
multichannel audio including
stereo, mono, and second
audio programming (SAP).
Standard aural IF is achieved
by heterodyne conversion of
the modulated intercarrier
signal with the visual IF.
IF Processing
The visual and aural
modulated IF signals are
combined and applied to IF
processing stages. These
stages provide outstanding
signal precorrection to yield
a very linear transmitter
output. Amplitude
linearity, incidental carrier
phase modulation (ICPM),
and frequency response
correction are all
adjustable.
Upconversion
The IF signal is upconverted
to final channel frequency
through heterodyning with a
very stable local oscillator.
The oscillator is crystal and
oven temperature controlled
for excellent frequency
stability. The exciter is
controlled with an Automatic
Level Control (ALC) loop
which ensures stable signal
levels. After upconversion
the signal is amplified to
provide the exciter output.
Power Amplifiers
The parallel 600 watt
power amplifiers are high
gain units (45-50 dB),
which provide redundant
paths from the exciter to the
output. Redundancy is
enhanced with independent
power supplies and cooling
for each amplifier assembly.
The output stage of each
amplifier module utilizes
eight transistors in parallel for
added redundancy and on-air
reliability.
A high degree of protection
is provided with each
amplifier. Individual
circulators, overdrive
protection, VSWR cutback,
and overtemperature
protection are all included.
Automatic Gain Control
around each amplifier
ensures that the transmitter
output remains stable.
The output of each RF
cabinet is fed into a low loss
hybrid combiner. Output
bandpass and trap filtering is
included to provide superior
out of band rejection.